🐛Change check to see if amp-img has completed layout. (#21483)
🐛Change check to see if amp-img has completed layout. (#21483)

- Always use signals, since it should fire correctly after the layout callback for `amp-img` has completed (the image has been loaded).
cory-work/amphtml,nexxtv/amphtml,sebastianbenz/amphtml,cory-work/amphtml,jridgewell/amphtml,adup-tech/amphtml,zhouyx/amphtml,smartadserver/amphtml,cvializ/amphtml,ampproject/amphtml,media-net/amphtml,jmadler/amphtml,src-code/amphtml,sharethrough/amphtml,techhtml/amphtml,zhouyx/amphtml,taboola/amphtml,jridgewell/amphtml,lannka/amphtml,yandex-pcode/amphtml,zhouyx/amphtml,erwinmombay/amphtml,alanorozco/amphtml,prateekbh/amphtml,ampproject/amphtml,voyagegroup/amphtml,cory-work/amphtml,voyagegroup/amphtml,yandex-pcode/amphtml,cory-work/amphtml,jpettitt/amphtml,src-code/amphtml,ampproject/amphtml,tlong2/amphtml,jmadler/amphtml,honeybadgerdontcare/amphtml,sharethrough/amphtml,jmadler/amphtml,mhc-gh/amphtml,smartadserver/amphtml,smartadserver/amphtml,zhouyx/amphtml,erwinmombay/amphtml,jpettitt/amphtml,Gregable/amphtml,danielrozenberg/amphtml,Gregable/amphtml,media-net/amphtml,honeybadgerdontcare/amphtml,prateekbh/amphtml,honeybadgerdontcare/amphtml,dotandads/amphtml,jmadler/amphtml,media-net/amphtml,nexxtv/amphtml,Gregable/amphtml,cvializ/amphtml,dotandads/amphtml,honeybadgerdontcare/amphtml,prateekbh/amphtml,ampproject/amphtml,src-code/amphtml,techhtml/amphtml,dotandads/amphtml,smartadserver/amphtml,adup-tech/amphtml,honeybadgerdontcare/amphtml,rsimha-amp/amphtml,honeybadgerdontcare/amphtml,cory-work/amphtml,techhtml/amphtml,ampproject/amphtml,rsimha-amp/amphtml,yandex-pcode/amphtml,cory-work/amphtml,nexxtv/amphtml,zhouyx/amphtml,jpettitt/amphtml,tlong2/amphtml,zhangsu/amphtml,sebastianbenz/amphtml,taboola/amphtml,taboola/amphtml,adup-tech/amphtml,rsimha-amp/amphtml,sebastianbenz/amphtml,tlong2/amphtml,voyagegroup/amphtml,sharethrough/amphtml,ampproject/amphtml,jridgewell/amphtml,media-net/amphtml,jridgewell/amphtml,alanorozco/amphtml,taboola/amphtml,mhc-gh/amphtml,zhangsu/amphtml,tlong2/amphtml,danielrozenberg/amphtml,lannka/amphtml,alanorozco/amphtml,Gregable/amphtml,zhouyx/amphtml,taboola/amphtml,voyagegroup/amphtml,yandex-pcode/amphtml,prateekbh/amphtml,media-net/amphtml,rsimha-amp/amphtml,alanorozco/amphtml,jpettitt/amphtml,smartadserver/amphtml,zhangsu/amphtml,voyagegroup/amphtml,alanorozco/amphtml,taboola/amphtml,media-net/amphtml,dotandads/amphtml,src-code/amphtml,mhc-gh/amphtml,mhc-gh/amphtml,alanorozco/amphtml,jpettitt/amphtml,jridgewell/amphtml,jmadler/amphtml,mhc-gh/amphtml,sharethrough/amphtml,media-net/amphtml,lannka/amphtml,danielrozenberg/amphtml,alanorozco/amphtml,prateekbh/amphtml,smartadserver/amphtml,tlong2/amphtml,voyagegroup/amphtml,Gregable/amphtml,adup-tech/amphtml,sebastianbenz/amphtml,Gregable/amphtml,jpettitt/amphtml,rsimha-amp/amphtml,jmadler/amphtml,sharethrough/amphtml,techhtml/amphtml,mhc-gh/amphtml,nexxtv/amphtml,erwinmombay/amphtml,lannka/amphtml,yandex-pcode/amphtml,ampproject/amphtml,Gregable/amphtml,honeybadgerdontcare/amphtml,rsimha-amp/amphtml,lannka/amphtml,jpettitt/amphtml,zhangsu/amphtml,cvializ/amphtml,lannka/amphtml,techhtml/amphtml,zhouyx/amphtml,zhangsu/amphtml,danielrozenberg/amphtml,adup-tech/amphtml,cvializ/amphtml,lannka/amphtml,cvializ/amphtml,erwinmombay/amphtml,jridgewell/amphtml,yandex-pcode/amphtml,danielrozenberg/amphtml,danielrozenberg/amphtml,src-code/amphtml,danielrozenberg/amphtml,ampproject/amphtml,tlong2/amphtml,nexxtv/amphtml,sebastianbenz/amphtml,dotandads/amphtml,dotandads/amphtml,prateekbh/amphtml,cory-work/amphtml,danielrozenberg/amphtml,techhtml/amphtml,mhc-gh/amphtml,erwinmombay/amphtml,adup-tech/amphtml,rsimha-amp/amphtml,jridgewell/amphtml,cvializ/amphtml,zhangsu/amphtml,sebastianbenz/amphtml,mhc-gh/amphtml,yandex-pcode/amphtml,sharethrough/amphtml,nexxtv/amphtml,jpettitt/amphtml,src-code/amphtml,erwinmombay/amphtml,alanorozco/amphtml,taboola/amphtml,voyagegroup/amphtml,media-net/amphtml,nexxtv/amphtml,Gregable/amphtml,prateekbh/amphtml